This invention relates to a device for controlling the rotation of the stepping motor in a printer so as to stop the rotation of the stepping motor at a particular rotation angle.
Heretofore, in a matrix printing type serial printer as shown, for example, in FIG. 1, a printing type wheel 2 is mounted on the drive shaft 1 of the stepping motor M and the stepping motor M is driven to select a desired printing type to be used for a particular printing operation. However, in such a serial printer, in order to eliminate error in the printing type selection which may be caused by any improper stepping of the stepping motor, a particular rotation angle of the motor drive shaft 1 is detected as the reference rotation angle and the drive shaft 1 is returned to the particular or reference rotation angle in the manner hereafter described immediately after one printing operation has been completed.
That is, a detector 3 in the form of a bar is fixedly fitted on the drive shaft 1 of the stepping motor M and a U-shaped frame member 4 is fixedly secured to the carriage (not shown) on which the stepping motor M is mounted in such a position that the opposing legs of the frame member or the light emitting element L and light receiving element F surround a section of the rotational movement path of the detector 3 whereby the light emitted from the light emitting element L normally maintains in the ON position the light receiving element F and when the detector 3 intervenes between the light emitting and receiving elements L and F as the detector 3 rotates in its rotational movement path, the light receiving element F is turned OFF.
For returning the motor drive shaft 1 to the above-mentioned particular or reference rotation angle after one printing operation has been completed, first of all, the drive shaft 1 is rotated in one direction (as shown by the arrow in FIG. 2A) to thus cause the detector 3 to intervene between the light emitting and receiving elements L and F thereby turning the light receiving element F OFF (FIG. 2), which in turn stops the rotation of the stepping motor M and accordingly, of the drive shaft 1 thereof.
However, in such an arrangement of the serial printer, when the detector 3 is mounted on the motor drive shaft 1 in a position slightly deviating from the reference position in the clockwise or counter-clockwise direction, the time point at which the detector 3 passes over the reference rotation angle does not coincide with the time point at which the detector 3 intervenes between the light emitting and receiving elements L and F to interrupt the passage of the light emitted from the element L to the element F and thus there is the drawback that the drive shaft 1 of the stepping motor M tends to cease rotation at a rotation angle which deviates from the particular or reference rotation angle by one or two steps. In order to eliminate this drawback, it is necessary that the position of the detector 3 is finely adjusted by a tedious procedure.